Apparatus and method for controlling boiling conditions of hot phosphoric acid solution with pressure adjustment

ABSTRACT

Disclosed is an apparatus and method for controlling boiling condition of hot H 3 PO 4  solution by adjusting the vapor extracting rate thereof, wherein an acid tank filled with hot H 3 PO 4  solution to a level surface is located in a treatment room and a temperature thermocouple is arranged above the level surface of the hot H 3 PO 4  solution to monitor the vapor temperature near the level surface of the H 3 PO 4  solution. The vapor temperature is used to adjust the extracting rate of the treatment room by control of a damper connected to an outlet of the treatment room. According to the present invention, the treatment apparatus and method can control the boiling condition of the hot H 3 PO 4  solution thereof by properly adjusting the extracting rate, and therefore avoid defects and loss of control in manufacturing processes.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a treatment apparatusand method for hot phosphoric acid (H₃PO₄ ) solution, and moreparticularly, to an apparatus and method for controlling boilingconditions of hot H₃PO₄ solution by adjusting extracting rate thereof.

BACKGROUND OF THE INVENTION

[0002] H₃PO₄ has a lot of applications in industries, for example, inmanufacturing processes of integrated circuits formed withinsemiconductor substrates. It is always the case to make micro patternson wafers in the manufacture of the integrated circuits, in whichetching technique is the primary method for forming these patterns. Theetching process transfers the micro pattern of a photo resist preciselyrendered with lithography technique, in the form of lines, surfaces, orholes, to the material under the photo resist in order to form a complexstructure required by the integrated circuit. The pattern transfercombining the etching process and lithography technique therefore playsa vital role in the semiconductor manufacturing processes.

[0003] Silicon nitride (Si₃ N₄) is often used as a mask for formingfield oxide (FOX) during oxidation processes and passivation layer overa semiconductor device. Traditionally, Si₃ N₄ is etched by use of aspiking hot H₃PO₄ solution. To maximize the etching rate, deionized (DI)water spiking for the hot H₃PO₄ solution should be controlled and heatis provided by a heater so as to keep the H₃PO₄ solution in a specificboiling condition. The boiling condition of the hot H₃PO₄ solution canbe fine-tuned, which is done by checking whether or not the temperatureof the hot H₃PO₄ solution reaches the setting value and also by checkingthe boiling condition with visual inspection. In the etching processwith the hot H₃PO₄ solution, if the boiling condition is too violent,the wafer under etched will have undesired displacement; while if theboiling condition is insufficient, an ideal etching rate will not beobtained.

[0004] However, in the practical etching processes, even though theH₃PO₄ solution temperature is kept constant, the DI water spiking iskept constant, and the output of the heater is also kept constant, theboiling condition of the H₃PO₄ solution differs. That is, the H₃PO₄treatment cannot get the desired control, thus resulting in defects andloss of control in the manufacturing process. Therefore, it is desiredan improved apparatus and method for a better control of boilingconditions of the H₃PO₄ solution.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide an apparatus andmethod for controlling boiling conditions of hot H₃PO₄ solution to solvethe problem mentioned above.

[0006] According to the present invention, an apparatus for controllingboiling conditions of hot H₃PO₄ solution comprise an acid tank filledwith hot H₃PO₄ solution thereof and located in a treatment room. Atemperature thermocouple is arranged above the level surface of the hotH₃PO₄ solution to monitor the vapor temperature of the hot H₃PO₄solution, and a damper under control is connected to the outlet of thetreatment room so as to control the extracting rate of vapor from thetreatment room.

[0007] According to the method of the present invention, the vaportemperature measured by the temperature thermocouple above the levelsurface of the hot H₃PO₄ solution is used to determine the boilingcondition of the hot H₃PO₄ solution, which is in turn used to adjust theextracting rate of vapor from the treatment room in order to maintainthe desired boiling condition. Given the same heating condition and thetemperature of the hot H₃PO₄ solution being maintained constant, whenthe extracting rate is low, less heat is lost and the rate of heatdiffusion is low, so that the hot H₃PO₄ solution is in a violent boilingcondition. On the contrary, when the extracting rate is higher, moreheat is lost and the rate of heat diffusion is high, so that the H₃PO₄solution is in a gentle boiling condition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art uponconsideration of the following description of the preferred embodimentsof the present invention taken in conjunction with the accompanyingdrawings, in which:

[0009]FIG. 1 shows an illustrative diagram of a conventional apparatusfor an H₃PO₄ solution treatment in semiconductor manufacturingprocesses;

[0010]FIG. 2a shows an illustrative diagram of one apparatus embodimentaccording to the present invention with a treatment room connected to adamper set in full-open state; and

[0011]FIG. 2b shows an illustrative diagram of the apparatus shown inFIG. 2a with the damper closed.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The mechanism and principle of the hot H₃PO₄ treatment apparatusis first explained. A traditional H₃PO₄ treatment apparatus, as shown inFIG. 1, employs a closed or almost closed treatment room 11 with anoutlet 12 connected to a damper 13, from where the vapor of thetreatment room 11 is extracted out. An acid tank 20 filled with hotH₃PO₄ solution 21 to a level surface 22 is placed in the treatment room11. A heater 30 for providing heat to boil the H₃PO₄ solution 21 isarranged outside and close to the acid tank 20 and another heater(in-line heater, not shown in the figure) is positioned outside thetreatment room 11. To monitor the temperature of the hot H₃PO₄ solution21, a thermocouple 23 is dipped in the hot H₃PO₄ solution 21. A topcover 24 is placed above the level surface 22 of the hot H₃PO ₄ solution21, and DI water is guided into the acid tank 20 by a pipeline 40connected to the acid tank 20. An outer tank 50, which provides a cyclicheating route for the mixed solution 21 within the acid tank 20, ispositioned outside the acid tank 20. In addition, the mixed solution 21in the acid tank 20 is transferred by a pipeline 51 and extracted by apump, is filtered by a filter and heated by an in-line heater, and thenenters the cyclic path through the pipeline 40 at the bottom of the acidtank 20 to recycle.

[0013] In the practical manufacturing processes, the heater 30 providesthe heat to let the hot H₃PO₄ solution 21 be boiled and the boilingtemperature of the hot H₃PO₄ solution 21 is monitored by the temperaturethermocouple 23. Visual inspection also helps if the boiling conditionis to be checked. A wafer 60 is placed into the acid tank 20 and iscovered with the hot H₃PO₄ solution 21. The heater 30 heats the acidtank 21 and the input of the DI water into the acid tank 20 iscontrolled so that the hot H₃PO₄ solution 21 is kept in a specific andstable boiling condition. If the hot H₃PO₄ solution 21 boils violently,then the wafer 60 being etched will be moved; on the contrary, if thehot H₃PO₄ solution 21 boils insufficiently, then the ideal etching ratecannot be reached.

[0014] However, during the practical etching processes, even the outputof the heater 30 is kept constant, the temperature of the hot H₃PO₄solution 21 is kept constant, and the input of the DI water is also keptconstant, the hot H₃PO₄ solution 21 still shows different boilingconditions. That is, the hot H₃PO₄ solution 21 is either in violent orunder boiling condition, so that the wafer 60 being etched will beundesirably moved or the ideal etching rate cannot be reached. Bypractical experiments, it is found that the vapor-extracting rate at theoutlet 12 of the treatment room 11 has great impact on the boilingconditions of the hot H₃PO₄ 21 and must be well controlled.

[0015] The hot H₃PO₄ treatment apparatus according to the presentinvention is shown in FIG. 2a. In the treatment room 11, the DI water isinfused with steady input volume into the acid tank 20 via the pipeline40, and the heater 30 also has a steady output. The temperature of thehot H₃PO₄ solution 21 contained in the acid tank 20 is monitored by thetemperature thermocouple 23, as in the prior art; however, anothertemperature thermocouple 23′ is additionally arranged above the levelsurface 22 of the hot H₃PO₄ solution 21 to monitor the temperature ofvapor 26 evaporated from the hot H₃PO₄ solution 21. The temperaturemonitored by the thermocouple 23′ is used to adjust the heat diffusionfrom the outlet 12 by the control of the damper 13, typically abutterfly damper. For a better control, a pressure gauge 131 is furtherinstalled in front of the damper 13 so as to monitor the pressure at theoutlet 12. It is noted that a pressure gauge measures a pressurevariation from a reference pressure, so does the pressure gauge 131.Fine-tuning the damper 13 and thus controlling the extracting rate ofvapor from the treatment room 11 so that the hot H₃PO₄ solution 21 canbe maintained at desired boiling conditions.

[0016] The present invention employs the data gathered by thetemperature thermocouple 23′ to determine and control the boilingcondition of the hot H₃PO₄ solution 21 by opening the damper 13 wider ornarrower. For such circumstances, when vapor is extracted from thetreatment room 11, a negative pressure is read on the pressure gauge131. As shown in FIG. 2a, the damper 13 is in full-opened condition, sothat the extracting rate is maximized and the absolute value of thepressure measured by the pressure gauge 131 is also maximized (based onBernoulli law). At this time, the heat diffusion rate of the acid tank20 is maximal, so the hot H₃PO₄ solution 21 cannot get enough heat andconsequently it will not be sufficiently boiling.

[0017]FIG. 2b shows an illustration of the apparatus of FIG. 2a with thedamper 13 is in full closed condition. When the damper 13 is in theclosed condition or is in a slightly opened condition, the pressurevalue measured by the pressure gauge 131 is very low, which means thatits extracting rate is also very low. At this time, the heat diffusionrate of the acid tank 13 is small, so the H₃PO₄ solution 21 has enoughheat to be maintained in a sufficient boiling condition.

[0018] The data acquired from experiments, which is done according tothe apparatus of FIGS. 2a/2 b, is shown as following table: TABLE 1 Bathheater (30) O/P  95%  95%  95% In-line heater O/P 100% 100% 100% Outletpressure (131) −20 −10  −5 Ex-acid pressure (mm-H₂O) Solutiontemperature thermocouple 160 160 160 (23) T/C 1 (° C.) Vapor temperature55˜67 77˜82 88˜93 thermocouple (23′) T/C 2 (° C.) Etching rate to Si₃N₄(A/min)  43  50 NA Visual boiling condition No boiling Gentle Violent

[0019] During the experimental etching processes, the output of theheater 30 is kept constant (95%) and the output temperature of thein-line heater is also kept constant (100 %). Given the measure of thetemperature thermocouple 23 and the condition in which the temperatureof the hot H₃PO₄ solution 21 is kept constant (160° C.) and the input ofthe DI water (not shown in the table) is also kept constant, thetemperature measured by the thermocouple 23′ and the (negative) pressuremeasured by the pressure gauge 131 at the outlet 12 can be used toadjust the pressure-extracting rate of the damper 13. As shown in Table1, when the vapor temperature measured by the thermocouple 23′ is in therange of about 55-67° C., the measured pressure of the pressure gauge131 at the outlet 12 is −20 mm-H₂O. At this time, the hot H₃PO₄ solution21 in the acid tank 20 is not in a boiling condition. However, when thevapor temperature measured by the thermocouple 23′ is in the range ofabout 7-82° C., the pressure of the outlet 12 is −10 mm-H₂O. At thistime, the hot H₃PO₄ solution 21 is in a gentle boiling condition. Whilethe vapor temperature measured by the thermocouple 23′ is in the rangeof about 88-93° C., the pressure of the outlet 12 is −5 mm-H₂ O. At thistime, the hot H₃PO₄ solution 21 is in a violent boiling condition. Thatis, given the same heating condition and the temperature of the hotH₃PO₄ solution 21 being kept constant, the more the negative pressure131 measured at the outlet 12 is, the lower the vapor temperaturemeasured is. On the contrary, the less the negative pressure 131measured at the outlet 12 is, the higher the vapor temperature measuredis. It can be concluded that by adjusting the damper 13 to control thevapor extracting rate of the treatment room 11, the hot H₃PO₄ solution21 can be precisely controlled and maintained in expected boilingconditions so as to reach the best etching rate for the wafer 60 andavoid defects and loss of control during the manufacturing processes.

[0020] While the present invention has been described in conjunctionwith preferred embodiments thereof, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, it is intended to embrace all suchalternatives, modifications and variations that fall within the spiritand scope thereof as set forth in the appended claims.

What is claimed is:
 1. An apparatus for controlling boiling condition ofhot H₃PO₄ solution with pressure adjustment, comprising: a treatmentroom with an a outlet; an acid tank located in said treatment room forfilling with hot H₃PO₄ solution to a level surface; a heater forproviding heat to said hot H₃PO₄ solution; a pipeline connected to saidacid tank for guiding DI water into said acid tank; a temperaturethermocouple arranged above said level surface for monitoringtemperature near said level surface; and a damper connected to saidoutlet for controlling vapor-extracting rate of said treatment room. 2.An apparatus according to claim 1, further comprising a secondtemperature thermocouple dipped in said hot H₃PO ₄ solution formonitoring temperature of said hot H₃PO₄ solution.
 3. An apparatusaccording to claim 1, further comprising a top cover placed above saidlevel surface of said hot H₃PO₄ solution.
 4. An apparatus according toclaim 1, further comprising an external tank outside said acid tank forproviding a cyclic heating path for said hot H₃PO₄ solution in said acidtank.
 5. An apparatus according to claim 1, further comprising apressure gauge arranged near said damper.
 6. A method for controllingboiling condition of hot H₃PO₄ solution, comprising the following stepsof: heating hot H₃PO₄ solution filled to a level surface in an acid tankof a treatment room having an outlet connected with a damper; measuringa vapor temperature near said level surface of said hot H₃PO₄ solution;and adjusting a vapor-extracting rate of said treatment room accordingto a variation of said vapor temperature.
 7. A method according to claim6, further comprising maintaining a solution temperature of said hotH₃PO₄ solution in a specific range.
 8. A method according to claim 6,further comprising maintaining said vapor temperature in a specificrange.
 9. A method according to claim 6, wherein said extracting rate ishigher when said vapor temperature is increased.
 10. A method accordingto claim 6, further comprising monitoring a pressure near said outlet ofsaid treatment room.
 11. A method according to claim 6, furthercomprising guiding a DI water into said acid tank at a steady inputrate.